1. Field of the Invention
This invention relates to liquid, preferably sprayable, compositions containing biologically active material, particularly those that are useful in agriculture. These compositions provide for the release and often for the sustained action of biologically active substances. More particularly, the invention relates to a preferably sprayable liquid product that is formulated with a biologically active substance such as a herbicide or other pesticide for use in crop production. This product can be applied to the soil or plant foliage using conventional equipment. Its composition is such as to provide prolonged activity or improved activity.
2. Description of the Prior Art
Melamine and its hydrolysis products, ammeline, ammelide, and cyanuric acid, and as well the related material dicyandiamide (cyanoguanidine), have often been considered as potential sources of nitrogen for incorporation in fertilizer compositions or for utilization as nitrogen sources per se. Melamine and dicyandiamide each have a nitrogen content of 66.67%; two-thirds of their weight is nitrogen. When used as fertilizer materials, they provide high percentages of nitrogen per unit weight applied.
Commercially produced melamine is available only as a fine crystalline powder, because small size particles are required for the present major commercial end markets for melamine. A typical screen analysis for one commercially available (from Melamine Chemicals, Inc.--MCI) dry melamine product, conducted with United States Standard Sieve screens, is as follows:
______________________________________ Percent Screen Analysis Retained ______________________________________ 40 Mesh 0-0.1 40-50 Mesh 0-0.1 50-60 Mesh 0-0.3 60-80 Mesh 0.5-5.0 80-100 Mesh 1.0-5.0 100-200 Mesh 13-30 200-325 Mesh 13-30 Thru 325 Mesh 40-60 ______________________________________
Other commercially available melamine products may be somewhat coarser, but the majority of the particles remain below 40 mesh. The smallest particles are very fine and powdery, and their sizes are difficult to measure. The fine particle sizes of commercial dry crystalline melamine, as currently produced, make it difficult to use as such, as a dry fertilizer material. An aqueous slurry of particulate melamine is suggested for use in the Freepons application, above, for dispensing into a trench, where the fine melamine particles can easily be covered by a layer of soil, so they will not blow away.
A somewhat related agricultural chemical problem is the formulation of biocides, plant growth regulants, and other biologically active materials for slow or controlled rate release, and for improved efficacy. Biocides include such pesticides as insecticides, herbicides, and fungicides. One basic purpose of prolonged activity formulations of biocides is to extend the time between repeat applications and thus effect a saving on the cost of the labor involved in an application. A second important purpose is to improve the effectiveness of a biocide by a sustained but more uniform activity over a period of time, rather than the inefficient technique of several applications of the biocide alone, over a period of time, with concomitant short periods of high biocide concentration and effectiveness together with the risk during such periods of pollution and phytotoxicity to crops, and long periods of low or zero concentration.
More prolonged activity for biologically active materials would permit extended time intervals between treatments and the reduction of the application level for a given effect over a period of time, thus reducing environmental impact. Thus, from an ecological standpoint, the controlled release of a pesticide, for example, if coupled with improved efficacy and a prolongation of effective activity, would enhance the lifetime of a non-persistent agent at the site of treatment.
When only ferilizer is applied to slow growing crops such as trees, weeds that compete with tree seedlings may be stimulated to grow to such an extent as to crowd and compete with the seedlings. Thus the positive effects expected from fertilization may be negated by the vigorous growth of weeds that compete with the trees for vital water, light, and nutrients. Also, if fertilizer materials such as urea and/or ammonium salts are applied in sufficient quantity so that the effects can be observed over a significant period of time, not only is fertilization inefficient but also there may be toxic effects because of salt stress. Avoiding this by more frequent multiple, small applications generally is not practical for tree crops.
The controlled release of biocides has previously been achieved by their incorporation within a matrix of a synthetic polymer, e.g., encapsulation wherein for example a pest control agent is surrounded by an enveloping wall of a synthetic polymer that permits loss through diffusion, permeation or degradation; dispersion of the pesticide in an elastomer or a synthetic plastic wherein the pesticide is released through leaching or diffusion; or chemical combination of the pesticide with a high molecular weight synthetic polymer in such a manner that the appended pesticide is slowly released from the polymeric backbone upon exposure to the pest infested environment. However, the prior art approaches often fall short of what is desired, in one or more respects. Also, they tend to be expensive, and some of the synthetic polymeric materials suggested for use are either not biodegradable or degrade so slowly that it is not a useful property.
Some sustained action, biologically active compositions, such as insecticides, fungicides, herbicides, nematocides, and other biocides, and plant growth regulators, are disclosed in U.S. Pat. No. 3,074,845 to Geary. The biologically active material is formulated with an inert carrier material and an amido-aldehyde resin. The formulation is prepared by first impregnating the inert carrier material with the biologically active substance, coating the impregnated carrier material with the amido-aldehyde resin, and then polymerizing the resin in situ. Suitable resins include urea-formaldehyde, melamine-formaldehyde, and urea-melamine-formaldehyde resins.
A later Geary patent, U.S. Pat. No. 3,223,513, discloses similar sustained release compositions in which the biologically active material is mixed with monomeric amido and monomeric aldehyde reactants, and then the reactants are polymerized to form an amido-aldehyde resin in situ. When the biologically active material and the resin-forming reactants are combined, an occlusion of the active material with the resin is obtained, which in physical form is sieve-like or sponge-like in structure with the molecules of active material in the interstices of the polymer.
Belgian Pat. No. 885,166, of Allan (the applicant herein), discloses a simple physical mixture of fine particles of (1), melamine that has been recrystallized to remove certain phytotoxic impurities and (2), a controlled release form of 2,4-dichlorophenoxyacetic acid (2,4-D). The preferred controlled release form of 2,4-D is prepared by intimately mixing or melting together equal parts by weight of kraft lignin and 2,4-D and extruding the resulting mixture in pellet or flake form of the desired size.
More recently, U.S. Pat. No. 4,283,387 to Young et al. discloses controlled release biologically active compositions similar to those disclosed in the later Geary patent mentioned above. In Young et al., a mixture comprising a carbinol-containing organic polymer, crosslinking agents for the polymer, and a biologically active substance undergoes hydrolysis to form a polymeric network capable of controlling the release of the biologically active substance.
A different approach appears in Pierce, 3,172,752. In one embodiment, a herbicide, fungicide, or insecticide is mixed with activated sewage sludge. The mixture is then adsorbed into pores, some of which are capillary, in particles of expanded perlite. The particles are then sprayed with a urea-formaldehyde solution, which forms a very slowly soluble sheath about each particle upon curing and drying.